Technical Field
The present invention relates to photodiodes, and more particularly to photodiodes with a II-VI n-type layer to reduce fabrication steps and device complexity.
Description of the Related Art
Conventional InGaAs photodiodes include a p-type ohmic contact on one side of a p+ substrate (InP). An InGaAs intrinsic layer is formed on the substrate opposite the p-type ohmic contact. An n-type window layer (e.g., InP (Si doped)) is formed on the InGaAs layer, and an n+ contact layer (e.g., InGaAs (Si doped)) is formed on the window layer. An n-type ohmic contact is formed over the contact layer.
While this structure (n-i-p) provides good performance, there are some operational issues with the photodiode. For example, light absorption at the n+ contact layer results in device losses due to low band gap and low doping concentration in the n+ contact layer. In addition, dark current of the n-i-p photodiode is high. Dark current is the relatively small electric current that flows through a photosensitive device when no photons are entering the device. Incident radiation may enter from the n-type ohmic contact side. This n-type ohmic contact is generally comprised on an opaque metal and therefore needs a reduced footprint to reduce shadowed areas. The shadow areas reduce the performance of the device.